1. Field of the invention
The present invention is directed to device and method for storing ink for ink-jet printing, and is particularly directed to a flexible sheet material that covers the sides of a porous ink-containing member within an ink chamber.
2. Description of the Related Art
Ink-jet printers commonly employ ink-jet print cartridges, or "pens," which include a sophisticated printhead and an attached ink chamber filled with a supply of ink. The printhead is a micromechanical part that contains an array of miniature thermal resistors or piezoelectric transducers that are energized to eject small droplets of ink out of an associated array of nozzles. In some cases the printhead is permanently attached to the ink supply, and in others the ink supply can be separately replaced. The pen is mounted in a carriage in the printer where the pen electrically interfaces with the printer. The printer scans the pen back and forth across the print medium (e.g., paper) as the pen ejects small droplets from the nozzles in selected matrix patterns, to thereby print a swath of the desired alphanumeric characters or graphics. After each swath of printing, the printer advances the medium incrementally to begin a new swath. Successive swaths are printed in this manner to complete the desired alphanumeric characters or graphics on the medium.
The ink in the pen must be held in the ink chamber at less than atmospheric pressure, so that the ink does not drool out of the nozzles when the nozzles are not firing. However, this negative relative pressure, or backpressure, must not be so great that air is gulped into the interior of the firing chambers, thereby causing them to "deprime" and no longer function. Various mechanisms have been devised to provide the appropriate backpressure, such as resilient bladders and combinations of springs and flexible bags.
One of the most reliable backpressure systems uses a porous material, such as synthetic foam, in the ink tank. Ink is injected into the foam and the foam retains the ink at the appropriate backpressure by capillary action. U.S. Pat. No. 4,771,295 (Baker '295), which is assigned to Hewlett-Packard Company (the assignee of the present invention), discloses an ink-jet pen that uses synthetic foam for ink retention and backpressure. A key feature of the pen disclosed in Baker '295 is an ink pipe that extends upward from a bottom wall of the pen body and into compressive contact with the foam. The ink pipe is the fluid conduit for the ink from the foam to the printhead. The ink pipe locally compresses the foam to thereby increase the capillarity of the foam in the region of the ink pipe. As ink is depleted from the foam, the increased capillarity near the ink pipe tends to draw ink from all other portions of the foam toward the ink pipe, so that the maximum amount of ink can be drawn from the foam for printing.
It has become increasingly important to make ink-jet pens as narrow as possible. The overall width of the pen influences the width of the printer and the amount of desk space the printer takes up. In addition, when printing with multiple pens, such as in color printing, print quality can be enhanced by making the pens narrower. Narrower pens allow the printheads of the pens to be more closely spaced so that during printing, as the pen is scanned across the print medium, less time goes by between ejection of the different colored droplets. On the other hand, users of printers desire that ink-jet pens last longer, in other words, that they hold more ink. Therefore, the designer of ink-jet pens must deal with the competing demands of making the pens narrower, and the need to increase the volume of ink contained in the pen.
One way of increasing the volume of ink while maintaining a narrow profile is to make the pen taller. In foam-based pens, the foam is typically loaded down from the top of the pen body, so that when the foam reaches the bottom of the pen, it will be in compressive contact with the ink pipe. However, with pens that load the foam from the top down into the pen, the taller the pen is, the more likely it will be that undesirable wrinkles or other anomalies will form in the foam as the foam is loaded into the pen. Such localized wrinkles and anomalies introduce unintended regions of higher compression. These regions of increased compression will have a higher capillarity than the surrounding foam, and ink will be "stranded" at these locations. Ink thus stranded is wasted and will not be available for printing. Also, the taller the pen is, the more chance there is that friction between the foam and the interior walls of the pen body during insertion will impede the desired compressive force between the foam and the ink pipe.
There remains a need for a foam-based ink-jet pen that allows for an ink chamber having a tall narrow aspect ratio without the associated problems of foam wrinkling and unstable seals between the foam and the ink pipes.